This is about my VW Polo (mk4). It's been a cat C in the past after taking a knock to the front bumper.

It needs the coolant topping up every six weeks (ish). I've been carrying a bottle of water in the car for this reason. It takes about 75cl to top it up to max when it's empty. When it happens the engine temperature warning light comes on (red) on my dash after driving for two minutes and the level is below minimum. I've been keeping an eye on the coolant level, it can be on max for weeks, then suddenly below minimum.

I've had it in the garage in the hope they can find a leak, or a crack. They say it's sealed tight with no damage or leaks that they can find. My radiator is in good condition. It's not smoking from the exhaust, so I don't think I'm burning it off. Removing the oil cap - the underneath is not white or milky.

Is there anything I can do? I'd rather not take it to the dealers for diagnosis, but it looks like I'm going to have to now.

  • You could try adding some Radweld - just a tiny bit as it's a small leak (assuming your coolant is water / antifreeze mix). It's ot best practice as too much of it blocks the coolant waterways but it would probably work. Dec 4, 2014 at 14:16
  • If you're losing it over the span of 6 weeks, you won't notice any white smoke from the exhaust. Not to alarm you, but my Subaru Forester blew a head gasket and I didn't ever see any white smoke (except on the day my wife followed me to the workshop and said she saw a tiny puff one time I pulled away). I would suggest having a leakdown test done on your cylinders. It doesn't test the cooling system for leaks, it tests the cylinders. Feb 2, 2015 at 13:29
  • But he would see coolant in the oil if the gasket is leaking, wouldn't he? Maybe it's evaporation through the radiator cap. Dec 23, 2015 at 8:25
  • Start with the simple and cheap stuff. Replace the cap on the expansion bottle with a new one. Should only be a small amount for the dealership. The cap has a rubber seal underneath which can perish. Jun 15, 2016 at 8:32
  • One other thing. When you add coolant to the system, you have got the heating controls set to "HOT" haven't you? If not, you can trap air in the cars heater matrix which is eventually released and finds it's way to the top of the expansion bottle. Jun 15, 2016 at 8:33

2 Answers 2


You can do a carbon momoxide test on the coolant system to see if you have an internal leak from your engines cylinders. Search on YouTube for 'How to test head gasket failure using an antifreeze HC Tester'.


had same problem on Polo 2008. Found leaking expansion tank: when is full and hot it starts leaking slightly through the middle joint. I noticed it only when topped up right to the MAX line. need to look carefully to see it. hoe it helps

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